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Broad-spectrum biofilm inhibition by a secreted bacterial polysaccharide.

The development of surface-attached biofilm bacterial communities is considered an important source of nosocomial infections. We hypothetisized that a better understanding of commensal/pathogen interactions within bacterial community could lead to an improved control of exogenous pathogens. In order to reveal adhesion or growth-related bacterial interference, we investigated interactions between uropathogenic and commensal Escherichia coli in mixed in vitro biofilms (Fig.1).
We demonstrated that the UPEC strain CFT073 and most extraintestinal E. coli as well as some other mucosal pathogens, secrete and release in the extracellulmar medium a specific type of capsular polysaccharide, the group II capsule, which displays a striking anti-adhesion activity toward both Gram positive and Gram negative pathogens (Fig.1).
While bacterial capsule has been proposed to be the outermost cell surface protective structure at the interface between the bacterium and its environment, our study demonstrates,that soluble, secreted "capsule" also modulate bacterial adhesion to surfaces and contribute to competitive interactions within bacterial communities (bacterial interference) (Fig.2). Using an interdisciplinary approach, we also show that the treatment of abiotic surfaces with capsular polysaccharides induces physico-chemical alterations, which prevent biofilm formation.
These findings identify capsular polymers as a new, non-antibiotic tool for bacterial adhesion contro, which may prove to be of significance in the design of new strategies to limit biofilm formation on medical indwelling devices.

 Valle, J. : Da Re, S., Henry N. ; Fontaine, T.; Balestrino, D.; Latour-Lambert, P.; and Ghigo J.M. (2006) Broad-spectrum biofilm inhibition by a secreted bacterial polysaccharide. Proc Natl Acad Sci U S 103:12558-12563.




Identification of new anti-biofilm polysaccharides.

We hypothesisized that the biofilm lifestyle could trigger metabolic adjustments potentially leading to the production of biofilm-associated molecules involved in competitive or cooperative behaviors affecting population dynamics. We screened a large collection of natural strains representative of E. coli species biodiversity and we showed that anti-adhesion compounds, which are not detected in non-concentrated planktonic supernatants, are frequently found in mature biofilm extracts (Fig.4). One of these compounds corresponds to a new type of released high-molecular weight polysaccharide, which induces increased surface hydrophilicity and confers a competitive advantage to the producing strain against clinically relevant Gram-positive bacterial pathogens such as Staphylococus aureus. This study showed that bacterial biofilms constitute untapped sources of natural bioactive molecules antagonizing adhesion or biofilm formation of other bacteria. The exploration of the biofilm environment could therefore provide a better understanding of bacterial interactions within complex communities and could lead to the identification of compounds permitting improved control of pathogen colonization. A structure function analysis of the identified anti-biofilm polysaccharides is under way.


• Rendueles, O. ; Travier, L. ; Latour-Lambert, P. ; Fontaine, T. ; Magnus, J. ; Denamur, E.  and Ghigo J.M. (2011) Screening Escherichia coli species biodiversity reveals new biofilm-associated anti-adhesion polysaccharides. mBio 00043-11.